AppNexus thinks there'll soon be just 3 places you need to go to buy video ads: YouTube, Facebook, and AppNexus

AppNexus, the pre-IPO US-based ad tech company, announced it is partnering with video ad tech firms including Teads and StickyAds to create an "open outstream video marketplace."

Outstream video ads are those users see appear on a page as they are scrolling through an article, which start playing automatically without sound. Users can dismiss or scroll away from the video if the ad doesn't appeal to them. An open marketplace means advertisers can buy these sorts of ads across a variety of different publishers websites, including those that don't currently offer video advertising inventory.

In the announcement press release, AppNexus says the marketplace will provide one of the "largest pools of programmatic outstream units." The company is hoping that the launch, coupled with its programmatic video capability launch last year (which allows marketers to buy more traditional, in-stream ads that sit within video players,) will mean that in the not-to-distant future, advertisers will only need to go to three destinations to buy online video ads: AppNexus, YouTube, and Facebook. Of coure, there are plenty of other players outside Facebook and YouTube that sell video ad inventory — TubeMogul and Tremor Video, for example — but AppNexus is pushing the scale of its marketplace versus other platforms.

Speaking to Business Insider, AppNexus president Michael Rubenstein said: "YouTube and Facebook have made their bets around a very closed approach to video advertising. And it's not actually about quality. The quality is actually quite poor — there are so so many cat videos on YouTube, s you know. It's because they have quantity. What's really cool about this [outstream video marketplace launch] is not just quality inventory and quality brands, but a really open approach to integrating with all kinds of companies, technologies, and techniques. I think that's where we typically draw the line with our business: taking open technology approach to a new market, and creating a real supermarket for video advertising."

US marketer spend on programmatic video advertising (video ads bought through automated, technology-driven methods such as through the AppNexus platform) is set to grow 84.5% year-on-year to $5.37 billion in 2016, according to eMarketer.

Rubenstein said he hopes the launch of a large outstream video marketplace will boost this spend even further as it allows a lot of non-traditional video publishers to become sellers of video advertising (because the ads appear in the "stream" as users scroll down, rather than having to sit within a video player.)

Here's a video from AppNexus explaining how the outstream video marketplace will work: